Optical systems are presently being employed in the communication of voice and video information as well as in the high speed transmission of data. Optical communication systems are desired because of the wide bandwidth available for the information signal channels.
Although this wide bandwidth is available, many of the existing optical fiber systems use only a single channel per optical fiber. Typically, this channel is transmitted at a wavelength of 1310 nm in one direction from a transmitting end to a receiving end and requires a second optical fiber to achieve bi-directional communication, however, recent increase in telecommunications traffic has resulted in a need for further fiber resources. One way this need was met, was to install additional optical fiber cables. Another was to increase the number of channels carried by same fibers.
Recently, technologies that can add additional channels to existing optical fiber cables already in the ground, have gained acceptance. These technologies seek to provide more than one channel on a single existing optical fiber and are therefore aimed at enhancing the efficiency of the existing fiber optic cable network. These technologies include wavelength division multiplexing (WDM) and bi-directional transmission.
When a number of wavelengths are multiplexed and transmitted on a single optical fiber, customarily, these channels must later be demultiplexed into separate channels or wavelengths of light. For example, it may be cost effective to transmit signals of wavelength .lambda.1, .lambda.2, .lambda.3, .lambda.4, .lambda.5, and .lambda.6 (.lambda. denoting a wavelength, lambda) along a single optical fiber, however, demultiplexing means are required to separate the light into six separate channels. Of course, it is desired to perform this demultiplexing at a minimum cost and with as little signal loss as possible.
Various types of optical filters have been contemplated and used to separate light of differing wavelengths. Unfortunately, coupling and other losses associated with many of these arrangements have led to devices that are less than satisfactory. For example, dichroic filters arc widely used as WDM devices; however, the reduction of channel spacing as well as the passband is limited by the current interference filter technology.
As of late, in-fiber Bragg gratings have become more prevalent in the field of fiber optics. An optical system utilizing Bragg gratings in combination with an optical circulator is shown in U.S. Pat. No. 5,283,686 issued Feb. 1, 1994 in the name of David Huber and assigned to General Instrument Corporation, Jerrold Communications, Hatboro, Pa. However, there are certain problems with the use of Bragg gratings alone; for example, the coupling losses in utilizing Bragg gratings and circulators alone as a means of multiplexing/demultiplexing in high density applications may in some instances be prohibitive. Furthermore, low yield, and cost are further disadvantages.
It is an object of this invention to provide a multi-channel demultiplexor that is capable of demultiplexing a multi-channel signal with less loss than known prior art demultiplexors and or multiplexing a plurality of channels into a single signal more conveniently and with less loss than in many other prior art devices.
It is a further object of the invention to provide a multi-channel demultiplexor that is configured in a manner to minimize loss normally associated with serial-type architectures.